Launch Safari 3.1 and navigate to http://cn.msn.com
Wait for the page to load fully.
Now click on the vertical/horizontal scrollbars.
Observe that the page does not scroll. It does scroll
with the mousewheel.
Debugged this and found that the mouse down event is handled by the
node returned as a result of the hit test. The hit test does not have
a scrollbar associated with it. This causes the page to not scroll.
The code should also check if there is a scrollbar under the mouse and
pass it off if yes. The webkit code already does this in the case when
the mouse down event is not handled.
Will submit a patch for this.

Comment on attachment 21113[details]
The patch containing the proposed fix for this issue.
For this to get checked in, we'll need a test case demonstrating the problem, in the form of a regression test.
I can't tell from reading the patch alone if this is correct. The test case will both help me understand that there truly is a bug here, and also is required as part of our "all bug fixes must have a regression test" policy.
To simulate a mouse click, you can use the eventSender feature of the regression test engine. The test in fast/events/mousedown_in_scrollbar.html is an example of one that tests a mouse event in a scrollbar, and could be used as a starting point in making a test.

I think the change looks ok (I am not a reviewer) since MouseEventWithHitTestResults does not set "scrollbar" when hit-testing a frame scrollbar, but only in-frame scrollbars (like scrollable <div>, <textarea>, etc).
(In reply to comment #3)
> Created an attachment (id=21113) [details]
> The patch containing the proposed fix for this issue.
However I could not reproduce the problem on Safari (webkit - trunk) on Snow Leonard. Given PLATFORM "WIN XP", I think it is Windows specific. Could you confirm?

(In reply to comment #0)
> Launch Safari 3.1 and navigate to http://cn.msn.com
> Wait for the page to load fully.
> Now click on the vertical/horizontal scrollbars.
> Observe that the page does not scroll. It does scroll
> with the mousewheel.
Safari seems to scroll the page ok now.
Please provide a (reduced) test case or a new URL that shows the bug or it is not actionable.
> Debugged this and found that the mouse down event is handled by the
> node returned as a result of the hit test. The hit test does not have
> a scrollbar associated with it. This causes the page to not scroll.
> The code should also check if there is a scrollbar under the mouse and
> pass it off if yes. The webkit code already does this in the case when
> the mouse down event is not handled.
>

Created attachment 209805[details]
Reduced test case
This bug is occurring on http://acko.net/ anywhere at the top. Debugging confirms a document mousedown handler fires when clicking the scrollbar. Emptying out the entire DOM does not fix this.
This is on Mac OS X, both with and without permanent scrollbars enabled. When using temporary scrollbars, you can also click the Gear button in the top right through the scrollbar.
I've attached a reduced test case. Note:
1) The scrollbar is unusable with the mouse
2) The grey div punches through the scrollbar for hit testing
Bug appears on Safari 6.0.5, Chrome 29, Chrome 31.

Attachment 273012[details] did not pass style-queue:
ERROR: Source/WebCore/ChangeLog:8: You should remove the 'No new tests' and either add and list tests, or explain why no new tests were possible. [changelog/nonewtests] [5]
Total errors found: 1 in 2 files
If any of these errors are false positives, please file a bug against check-webkit-style.

Created attachment 273040[details]
Archive of layout-test-results from ews106 for mac-yosemite-wk2
The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews106 Port: mac-yosemite-wk2 Platform: Mac OS X 10.10.5

Created attachment 273085[details]
Archive of layout-test-results from ews105 for mac-yosemite-wk2
The attached test failures were seen while running run-webkit-tests on the mac-wk2-ews.
Bot: ews105 Port: mac-yosemite-wk2 Platform: Mac OS X 10.10.5